Defects in tissue are often combined with an opening in a tissue such as in the blood vessel wall and organ tissues, like the septum in the heart of mammals, for example, atrial septal defect (ASD) and patent foramen ovale (PFO) as shown in FIG. 1. FIG. 1a shows normal septa between the right atrium (1) and the left atrium (2).
During the fetal development, the septum primum (3) starts to grow downward from the roof to divide the atria into two chambers, leaving a hole in the center called ostium secundum (4). A second septum, septum secundum (5), starts to develop on the right atrial side of the septum primum (3) and normally completely covers the ostium secundum (4) and, thereby resulting in a closed foramen ovale (6). However in some cases, incomplete coverage results in a hole (an opening) permitting blood flow in either direction (left-to-right or right-to-left), also known as an atrial septal defect. This atrial septal defect is also called secundum ASD (7). An example of such an atrial septal defect is shown in FIG. 1b. Even after normal formation of the septum secundum (5), an opening foramen ovale—remains between the septa in the fetus, functioning as a one-way (right-to-left) valve. This opening allows blood to follow from right atrium (1) to left atrium (2), bypassing the lungs in utero. At birth, changes in atrial pressures leads to apposition of the septa. Complete sealing of the opening happens within hours of birth. However, a patent foramen ovale, also called PFO (8), remains for about 25% of the total population. This situation is shown in FIG. 1c. ASD accounts for 25-30% of congenital heart defects that are diagnosed in adult hood, among which the majority are Secundum ASD (about 75%, located in the region of the fossa ovalis). The associated symptoms are most often exertional dyspnoea or fatigue and subsequent morbidity includes right ventricular dysfunction and failure, atrial tachyarrhythmias, or stroke. Clinical significance of PFO is still much debated; however, even a small, untreated patent foramen ovale can cause heart-related difficulties such as labored breathing or recurrent respiratory infections. Other medical conditions, such as migraine headaches, have also been associated with a PFO. PFO is also considered a possible risk factor for stroke and systemic embolism because of the potential formation of blood clots. These clots may form in veins and subsequently pass into circulation through the PFO, without being filtered in the lungs.
In general, treatment options include anticoagulant medication, surgical closure and transcatheter device closure. The anticoagulant therapy normally comprises the administration of aspirin, clopidogrel (Plavix), aspirin and clopidogrel together, and warfarin (Coumadin). Medication does not improve morbidity to a comfortable level and only reduces the risk of mortality. Surgical closure can be done safely and achieve extremely low mortality rate. But it does require open-heart surgery and an extracorporeal circulation system. Transcatheter closure is safe and effective for Secundum ASD and PFO. The entry is similar to a percutaneous cardiovascular intervention (PCI) procedure and is mostly done under the guidance of fluoroscope and transesophageal echocardiography (TEE). The minimum invasive surgery allows better patient compliance and faster recovery too.
The main current occluders for ASD and/or PFO closure are generally made of a metal frame (specifically made of Nitinol or Phynox) with synthetic fabrics (specifically made of polyster, Dacron or PTFE) or collagen matrix patches used as inserts. The metal frame usually has the form of an umbrella on each side of the opening combined by a metallic waist. The occluders are usually folded and inserted into a trans-luminal sheath, which is placed at the ASD/PFO location. Then the devices are deployed to seal the ASD/PFO under fluoroscopy and/or echocardiography.
After the ASD/PFO defect is closed by an occluder, a layer of ingrown tissue will usually cover the device and, will thus close the defect. Although elegant and smart device designs have been achieved owing to metal flexibility and excellent modulus, permanent presence of metal in the mammalian body leads to allergy and long-term toxicity risk. Metal-rich devices are also related to problems like friction lesions, perforations, erosion and thromboembolism. Furthermore, these devices made of metal and synthetic fabrics may obstruct the trans-septal access for the left atrium, which is of significant importance for the future treatment of left-sided heart disease including percutaneous heart valve repair or replacement, arrhythmia studies, and therapies (e.g., pulmonary vein exclusion and left atrial appendage closure).
Considering the above comments, it is therefore an object of the present invention to overcome at least some of the above-mentioned problems of existing occluders and to provide an alternative occlusion device for closing an opening in a tissue.